Chronic skin ulcers can be a persistent problem resulting from sustained oxygen deprivation of tissue, arising from a variety of root causes. Major causes include (i) mechanical pressure around bony prominences from long periods of bed rest preventing adequate blood flow (pressure sores), and (ii) the failure of non-return valves in the veins resulting in the pooling of blood in the legs when standing (venous leg ulcers).
The standard of care for treatment and prevention of chronic ulcers typically includes mechanical strategies to assist in the passage of blood to the affected tissues. In the case of pressure sores, regular movement of the patient to reduce the sustained pressure is often used, which may be assisted with electrically operated cushion supports that dynamically shift the pressure points. In the case of leg ulcers, elevation of the affected leg assists in drainage of the blood and compression bandages around the wound help to reduce swelling which in turn assists in peripheral blood flow.
Electrical stimulation of the affected area has been investigated for many decades as an aid in the healing of chronic ulcers. Despite many positive studies, electrical stimulation has not become broadly adopted as part of the standard of care, perhaps due to variability of research results and unresolved uncertainty as to the best form of electrical stimulation to apply.
The biological mechanism by which the electrical stimulation may operate to accelerate ulcer healing is uncertain, although early thoughts centred on the role of the “healing current” which has long been known to occur in a healing wound.
In an early study in 1976 Gault et al [Gault 1976] found that low intensity direct current approximately doubled the rate of healing of ischaemic skin ulcers. In 1988, Kloth et al [Kloth 1988] found in a small study of stage IV ulcers that pulsed monophasic high-voltage stimulation (twin peaked pulses, 105 Hz, 100 to 175 V, 45 minutes per day) with the electrodes applied either side of the wound, or over the wound if improvement plateaued, was able to eventually heal all 9 treated ulcers in a mean time of 7.3 weeks. In 1991, Griffin et al [Griffin 1991] in a study of monophasic high-voltage stimulation, pressure sores from 9 patients with spinal cord injury (twin peaked pulses, 100 Hz, 200 V, 1 hour per day, cathode placed over the wound) found that after 20 days reduction in wound area was 80% compared with a control group of 52% reduction. In 1991, Feedar et al [Feedar 1991] in a study of monophasic high current stimulation (132 μs rectangular pulses 29 mA, 64 Hz and 128 Hz) 14 treated ulcers (mainly pressure sores) reduced in size about twice as fast over a four week period as control ulcers (55% reduction versus 30% reduction).
In 1993, Wood et al [Wood 1993] in a multicentre double-blind study of pulsed low intensity direct current (300 μA DC pulsing to 600 μA at a frequency of 0.8 Hz) 43 treated stage II and stage III chronic ulcers reduced in size by an average of 85% over eight weeks compared to a rise in the control groups. Wood et al attributed the apparent higher success rate to reduced (sub milliamp) current on the basis that a current of about 600 μA was believed to be optimal for electrochemical healing parameters measured in animals.
In 1996, Baker et al. [Baker 1996] in a study on pressure sores compared high-voltage pulse stimulation (pulse width 100 to 300 μs, 50 Hertz) with a “sham” control of 4 mA 10 μs pulses at 1 Hz and a control of no stimulation and found that the high-voltage 50 Hz stimulation was more effective than the “sham” control and the zero stimulation control. The authors noted that the “sham” control appeared to have some activity, despite the very short 10 μs pulses, but drew no conclusions from that.
In 2003 Houghton et al [Houghton 2003] in a study on leg ulcers found that high-voltage poles stimulation (pulse width 100 μs's, 100 Hz, 150 V) for 45 minutes three times weekly over four weeks produced an average 44.3% decrease in wound area compared to 16% in sham controls.
From the above-mentioned prior investigations, it appears that the enduring popular treatment modality amongst investigators is high-voltage pulsed stimulation at a frequency between 50 and 100 Hz. Typically, the voltage applied is 100 V or more which would be expected to deliver well over 1 mA of current in most treatment situations. Such frequencies may be expected to stimulate the skeletal muscle, which could assist with mobilisation of blood and lymph flow. However, no satisfactory theory for the efficacy of such frequencies and currents is accepted and indeed the DC current results of Wood et al. described above are as good or better than the high frequency stimulation. DC currents are supposedly effective by virtue of electrochemical changes in the wound brought about by the constant direct current. In the absence of comprehensive double-blind studies directly comparing different methodologies, which among several currents and waveforms is optimum for the treatment of ulcers is unknown.
A massage protocol called manual lymphatic drainage (MLD) has limited efficacy in reducing accumulation of lymph (lymphoedema) and while it is sometimes used as part of the treatment modality for ulcers, MLD is not typically regarded as a major or strongly effective component in ulcer healing.
The background state-of-the-art therefore focuses on either electrochemical stimulation by DC currents or skeletal muscle stimulation by high frequency pulsed current.
The inventor believes that an electrical waveform targeted towards stimulation of the lymphatic system may have enhanced utility in the treatment of chronic ulcers, and that the importance of the lymphatic system has been underestimated in the treatment of ulcers.